Bilayer film including an underlayer having vertical acid transport properties

ABSTRACT

The present invention provides methods for forming images in positive- or negative-tone chemically amplified photoresists. The methods of the present invention rely on the vertical up-diffusion of photoacid generated by patternwise imaging of an underlayer disposed on a substrate and overcoated with a polymer containing acid labile functionality. In accordance with the present invention, the vertical up-diffusion can be the sole mechanism for imaging formation or the methods of the present invention can be used in conjunction with conventional imaging processes.

CROSS-REERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 10/334,219,which was filed on Dec. 30, 2002 now U.S. Pat. No. 7,160,665 for “METHODFOR EMPLOYING VERTICAL ACID TRANSPORT FOR LITHOGRAPHIC IMAGINGAPPLICATIONS.”

DESCRIPTION

1. Field of the Invention

The present invention relates to lithography, and more particularly tomethods for substantially minimizing the deleterious effects of highabsorbance (low transparency) in photoresist films employed in deepultraviolet (DUV) and extreme ultraviolet (EUV) lithographic imaging.More specifically, the present invention relates to the application ofvertical up-diffusion of photoacids generated in underlayers to improveimaging performance and resist profiles in semi-transparent chemicallyamplified resists.

2. Background of the Invention

In the semiconductor industry, there is a desire for higher circuitdensity in microelectronic devices made using lithographic techniques.Historically, this has been largely accomplished through a combinationof wavelength scaling (decreasing the wavelength of the imagingradiation), improvements in the imaging optics (employing lenses withhigher numerical apertures), and the use of higher performancephotoresists optimized for each new wavelength. The goal is to generateever-smaller photoresist features with the proper attributes (i.e.,vertical shape, etch resistance, etc.), which can then serve as reliefimages that enable the accurate transfer of a photoimage to theunderlying substrate. It is also a requirement that photoresists for 157nm and EUV lithography function at low exposure doses (have highphotospeeds) due to issues of tool throughput and source intensityconsiderations.

As the semiconductor industry (currently at 248 nm and 193 nmgenerations) moves to 157 nm and 13.4 nm technology, resist transparencybecomes a serious issue. The 157 nm resists currently under developmentare based on fluorinated polymers with absorbances of 1 to 3 μm⁻¹.Current generation EUV resists (based on phenolic polymers) have valuesof approximately 2 μm⁻¹. These values are much higher than found informulated DUV resists (with absorbances of approximately 0.2 to 0.4micron⁻¹) and pose significant problems for pattern profile control evenin the 1000 to 3000 Å thick films required for imaging sub-100 nmfeatures. For example, a change in film transparency from 65%(absorbance of 0.19) to 20% (absorbance of 0.7) has a very large impacton the feature profiles and results in features that have slopingsidewalls and incomplete development to the surface of the substrate.Degraded resist profiles of this type cannot be used in pattern transferapplications.

While major research activities are underway to improve resisttransparency at short wavelengths, particularly at 157 nm, it isunlikely that even the best short wavelength resists will be able toachieve the combination of transparency and etch resistance enjoyed bycurrent 193 and 248 nm resists.

There are a number of approaches in the prior art that can potentiallybe used to address the problem of poor resist profiles. These prior artapproaches include multi layer resist systems (also known as thin filmimaging resists) employing silicon based polymers or precursors(Willson, C. G. In Introduction to Microlithography 2nd Ed.; ACSProfessional Reference book, American Chemical Society, Washington D.C.;1994, Chapter 3; and Miller, R. D., Wallraff, G. M. in AdvancedMaterials for Optics and Electronics, 1994, 4, 95) can be used tocircumvent problems due to highly absorbing resists since imageformation occurs in a thin film (in the case of a bilayer resist seeU.S. Pat. No. 5,985,524 to Allen, et al.) or in the top surface of theresist. This image is then transferred to the underlying polymer via ananisotropic etch to yield patterns with vertical walls throughout thepolymer film(s). As such, this two stage process (imaging followed by O₂anisotropic etch) is fundamentally different from the standard singlelayer resist process in which the resist relief profile is generatedwithin a single polymer film.

Single layer resists are often used in conjunction with additionalpolymer films (disposed on top or beneath the imaging layer) to improveimage profiles. The primary use of these films is to circumvent problemswhich are not due to high absorbance but rather due to low resistabsorbance. These anti-reflection coatings (ARC's) (Levinson, H.,Arnold, W. In Handbook of Microlithography, Micromachining, andMicrofabrication, Rai-Choudhury Ed., SPIE Optical Engineering Press:Bellingham, Wash., 1997, 1, Chapter 1) are designed to minimizereflective notching, standing waves and other consequences due toreflectivity at the resist substrate interface. The presence of a bottomARC (the most prevalent type of reflectivity control system) canunfortunately introduce a different type of profile degradation notlinked to resist transparency but rather due to deleterious interactionbetween the ARC and the chemically amplified photoresist. Thisinteraction (sometimes termed as resist “poisoning”) can result as athin insoluble resist skin or “foot” at the base of the developedphotoresist image (positive tone resist). This effect can be minimizedthrough the incorporation of additives such as acids or photoacidgenerators. These materials are selected so as to have low diffusivityand thus provide little or no contribution to image formation within thetransparent resist film (see U.S. Pat. No. 5,939,236 to Pavelchek etal.).

Alternatively overcoated films containing diffusive basic additives havebeen disclosed (see Jung et al., Application 20010003030) to improve theimage profiles in highly absorbing films by neutralizing photoacid atthe top of the resist and thus creating a more uniform photoacidconcentration throughout the resist film. In this case, the top of theresist film is deliberately “poisoned” requiring that the resist beoverexposed (exposed at a higher imaging dose) to achieve verticalprofiles. This is an application of the well known consequences ofenvironmental contamination on photoresist profiles (see Hinsberg, W.D., Wallraff, G. M., Allen, R. D. in Kirk-Othmer Encyclopedia of Scienceand Technology Fourth Edition Supplement 1998).

None of the above mentioned approaches addressees the problem of poorresist profiles in high photospeed semi-transparent resists. It istherefore an object of the present invention to provide an improvedprocess for use in the imaging of semi-transparent resist materials.

SUMMARY OF THE INVENTION

The present invention provides methods for forming images in positive-or negative-tone chemically amplified photoresists. The methods of thepresent invention rely on the vertical up-diffusion of photoacidgenerated by patternwise imaging of an underlayer disposed on asubstrate and overcoated with a polymer containing acid labilefunctionality. In accordance with the present invention, the verticalup-diffusion can be the sole mechanism for imaging formation or themethods of the present invention can be used in conjunction withconventional imaging processes.

The extent of the vertical up-diffusion into the overlying photoresistlayer is dependent on the thickness of the photoresist layer. Typically,the extent of upward acid migration into the overlying layer willsubstantially extend beyond the resist: underlayer interface. Due tothis acid migration, the acid content present at the bottom portion ofthe overlying layer is preferably substantially equal to the content ofacid present in the upper portion of the overlying layer.

More specifically, the present invention relates to methods forgenerating an image in a bilayer film disposed on a substrate. Apreferred embodiment of the present invention comprises (A) anunderlayer comprising (i) a photoacid generator and (ii) a polymericmaterial that includes at least one of an organic polymer and aninorganic matrix material, wherein said photoacid generator is selectedto enhance vertical transport of generated acid into an overlying layer;and (B) a layer overlying said underlayer that comprises an organicpolymer containing acid reactive groups suitable for use in chemicallyamplified photoresists.

In broad terms, a preferred lithographic method of the present inventionincludes:

depositing an underlayer on a surface of a substrate, said underlayercomprising (i) a photoacid generator and (ii) a polymeric material thatincludes at least one of an organic polymer and an inorganic matrixmaterial;

irradiating the underlayer to generate acid throughout a patternedregion in the underlayer; and

transferring the pattern formed in the underlayer to a layer overlyingthe underlayer, said transferring comprising vertically transportingacid from the underlayer to the overlying layer to substantially enhancethe density of acid throughout the overlying layer, wherein sufficientacid is present in the overlying layer to permit lithographic patteringof the overlying layer, and wherein the photoacid generator is selectedto enhance said vertically transporting.

In accordance with the present invention, which may be advantageouslyused with conventional imaging systems, the density of acid at thebottom of the resist film in the overlying layer prior to acidtransference is less than that accumulated in the top portions of theresist film and generally below the threshold required for resistdevelopment. After acid migration, the density of acid is present morecontinuously from the top of the film to the bottom of the film.

The one or more radiation sensitive acid generators present in theunderlayer composition of the present invention are referred to hereinas a photoacid generator (i.e., PAG). The acid reactive groups presentin component (B) may comprise moieties such as esters, carbonates orketals which upon reaction with a generated acid are converted tocomponents that are soluble in photoresist developers. Resists based onsuch functionality are termed “positive-tone”. Other acid reactivegroups which may be present in component (B) are capable of undergoingprocesses such as crosslinking reactions which render such films lesssoluble to photoresist developers and are termed “negative-tone”systems.

The present invention is designed to ameliorate the problems encounteredwhen imaging photoresist films of marginal transparency. Conventionalsemiconductor lithography is based on the generation of a photochemicalimage of acid within the reactive polymer film and in the case ofabsorbing resist films the bottom of the film receives significantlyless light than does the top of the resist film. As a consequence, lessphotoacid is produced resulting in diminished reaction at the bottom ofthe resist film. By incorporating the inventive underlayer beneath aconventional photoresist, (e.g., the overlying layer) reaction may, insome embodiments, be achieved throughout the resist film. Otherembodiments are possible including a process in which the only source ofphotoacid is that produced in the inventive underlayer and the resistprofile is substantially determined by the acid catalyzed reactionresulting from the vertical up-diffusion of acid generated in theimagewise exposed underlayer. In a yet further embodiment of the presentinvention, the process relies on overcoating the acid liable polymer onan imagewise exposed underlayer subsequent to exposure. In this case,the transparency of the polymer topcoat is not an issue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are pictorial representations (through cross-sectionalviews) illustrating the method of the present invention through a firstprocessing scheme.

FIGS. 2A-2E are pictorial representations (through cross-sectionalviews) illustrating the method of the present invention through a secondprocessing scheme.

FIGS. 3A-3D are pictorial representations (through cross-sectionalviews) illustrating the method of the present invention through a thirdprocessing scheme.

FIGS. 4A-4B are scanning electron micrographs (SEMs) comparing the 157imaging using prototype 157 nm aromatic resist, in which FIG. 4A isrepresentative of the present invention (see Example 1) and FIG. 4B is acomparative example (see Comparative Example 1).

FIG. 5 is an SEM of another representative of the present invention (seeExample 3).

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a photoactive underlayer forimaging photoresist films, particularly semi-transparent photoresistfilms, will now be described in greater detail.

The photoactive underlayer of the present invention comprises one ormore photoacid generators (PAGs) and at least one of an organic polymerand an inorganic matrix material. The PAG component of the inventiveunderlayer is employed in amounts sufficient to generate a photoacid(s)concentration that is sufficient to effect acid catalyzed reactions overa significant depth of the overlying layer. Suitable amounts of the PAGspresent in the underlayer of the present invention range from about 0.5to about 20 weight percent, based on the total weight of the underlayer.More preferably, the PAG is present in the underlying composition in anamount of from about 0.5 to about 7.5 weight percent, based on the totalweight of the underlayer. Particularly preferred amounts of the one ormore PAGs will be a function of quantum yield, relative diffusivity, andacid strength, e.g., pK_(a), of the photoacids generated.

In addition, the selection of the PAG for use in the underlayer of thepresent invention is a function of the desired acid migration depth intothe overlying layer. This will be a function of the thickness of theoverlying layer, or a function of the extent of reaction due toconventional imaging. In the latter case, it is desired that thephotoacid generated in the underlayer have substantially differentproperties than the photoacid generated in the overlying layer byconventional exposure. More specifically, the PAG in the underlayershould generate a photoacid of higher diffusivity, preferably with equalor lower acidity than that employed in the overlying layer. PAGs used inconventional DUV photoresists are generally selected for their lowdiffusivity to minimize image blur; photoacid generators used in theunderlayer of the present invention require higher diffusioncoefficients that are tailored to the specific polymer in use.

Suitable acid generators that may be present in the underlayer includetriflates (e.g., triphenylsulfonium triflate or bis-(t-butylphenyl)iodonium triflate), pyrogallol (e.g., trimesylate or pyrogallol), oniumsalts such as a triarylsulfonium and diaryl iodoniumhexafluoroantimates, hexafluoroarsenates, trifluoromethane sulfonatesand others; iodonium sulfonates and trifluoromethanesulfonate esters ofhydroxyamines, alpha′-bis-sulfonyl diazomethanes, sulfonate esters ofnitro-substituted benzyl alcohols and napthoquinone-4-diazides and alkyldisulfonates. Other suitable acid generators for use in the underlayerare disclosed, for example, in U.S. Pat. Nos. 5,045,431 and 5,071,730both to Allen, et al. and Reichmanis, et al. review article (Chemistryof Materials, Vol. 3, page 395 (1991), the disclosures of which areincorporated herein by reference.

Preferred PAGs for use in the underlayer of the present inventioninclude, but are not limited to: onium salts (iodonium and sulfonium) ofperfluoroalkyl sulfonates, methides and imides, and other sulfonateesters. Mixtures of such PAGs are also contemplated to be present in theunderlayer of the present invention. Highly preferred PAGs for theunderlayer of the present invention are triarylsulfonium and diaryliodonium imides. (W. M. Lamanna, et al. included by reference. PROC SPIE4690 817 2002).

Other suitable PAGs that can be used in the underlayer composition ofthe present invention are disclosed in E. Reichmanis, et al., Chem.Mater, 1991, 3, 394; W. D. Hinsberg, et al. in Kirk Othmer Encyclopediaof Science Technology, Fourth Edition Supplement 1998, the disclosuresof which are both incorporated herein by reference.

The pK_(a) values of the acids generated in the underlayer arepreferably equal to or less than the pK_(a) values of the acidsgenerated in the overlying layer.

In addition to the one or more PAGs, the underlayer of the presentinvention also includes at least one of an organic polymer and aninorganic matrix material that preferably have absorbances less than orequal to 12 micron⁻¹. The organic polymer or inorganic matrix materialcomponent of the underlayer of the present invention preferably do notappreciably dissolve or intermix with the polymer topcoat during the topprocessing steps of coating and post apply bake. Suitable organicpolymers present in the underlayer of the present invention include:hard baked diazonapthoquinone (DNQ) novalac, polyimides, polyethers,polyacrylates and other organic polymers that are crosslinkable.Suitable inorganic matrix materials for use in the underlayer of thepresent invention include inorganic and/or hybrid organic/inorganicpolymers such as spin on silsesquioxanes (linear, branched or caged),hydridosilsesquioxoane, methylsilsesquioxoane and other Si-containingpolymers; commercial bottom anti-reflective coatings (ARCs) can also beused.

The underlayer of the present invention is generally cast from anorganic solvent. Suitable solvents for the underlayer include, but arenot limited to: propylene glycol mether ether acetate, cyclohexanone andethyl lactate.

The overlying layer of the bilayer film of the present inventionincludes any photoresist including positive-tone photoresists andnegative-tone photoresists that are capable of undergoing a chemicallyamplified reaction. Specifically, the chemically amplified photoresistsemployed in the present invention include at least a polymer resin.Generally, the polymer resins employed in the overlying layer arehomopolymers or higher polymers containing two or more repeating unitsand a polymeric backbone. The polymer resins present in the overlyinglayer typically contain polar functional groups such as hydroxyl.

Illustrative examples of suitable homopolymers that can be utilized inthe present invention include, but are not limited to:phenolic-containing resins such as poly(hydroxystyrene) including themeta-, para- or ortho substituted forms, and phenol formaldehydes;polymers having acid or an anhydride group, e.g., polyacrylic acid orpolymethacrylic acid; acrylamide; imide or hydroxyimides. Such polymerstypically have an average molecular weight of from about 1000 to about250,000.

With respect to the polymer resins that contain at least two monomerunits, the monomer units employed in such higher polymers are selectedfrom the group of hydroxystyrenes, styrenes, acrylates, acrylic acid,methacrylic acid, vinylcyclohexanol, phenol formaldehydes,methacrylates, acrylamides, maleic anhydrides and maleimides.

The polymer resins of the overlying layer may also contain a polymericbackbone such as, for example, polyolefins, polyolefin sulfones,polysulfones, polycyclic olefins, polycarbonates, polyimides,polyketones, polyethers and the like.

In some embodiments of the present invention, the polymer resin is anaromatic fluoroalcohol or other like fluorinated polymers which aresuitably used as 157 nm photoresists. Aromatic fluoroalcohols that maybe employed in the present invention are described, for example, inWallraff, et al. Proc. SPIE 1999, 3678, 138, the entire content of whichis incorporated herein by reference.

The polymer resins of the overlying layer also include acid reactivefunctional groups that are capable of undergoing a chemically amplifiedreaction upon exposure to radiation. These active groups are typicallyused to protect the polar groups of the polymer resin and aredeprotected therefrom during the imaging process. Depending on the typeof the acid reactive functional groups present in the polymer resin, theoverlying layer may function as a positive-tone chemically amplifiedresist or a negative-tone chemically amplified resist. When apositive-tone chemically amplified resist is employed as the overlyinglayer, the acid reactive functional groups that may be present on thepolymer resin include esters, carbonates, ketals, acetals, silyl ethersor mixtures thereof. Such acid reactive groups react with acid generatedupon exposure to radiation providing components that are soluble inphotoresist developers. The aforementioned acid reactive groups are wellknown to those skilled in the art; therefore a detailed description ofthe same is not need herein.

When the polymer resin is a negative-tone photoresist, the acid reactivegroups include reactive moieties such as alcohols that are capable ofundergoing a crosslinking reaction. The crosslinking reaction rendersthe polymer resin less soluble in a photoresist developer.

The fundamental processes and compositions used in chemically amplifiedphotoresists are well known to those skilled in the art and aredescribed, for example, in E. Reichmanis, et al., Chem. Mater, 1991, 3,394; W. D. Hinsberg, et al. in Kirk Othmer Encyclopedia of ScienceTechnology, Fourth Edition Supplement 1998, the disclosures of which areboth incorporated herein by reference.

In addition to the polymer resins which contain the acid reactivefunctional groups, the overlying layer may also include an acidgenerator and/or a crosslinking agent. The acid generators are typicallyfound in positive-tone photoresists, while the negative-tonephotoresists typically incorporate crosslinking agents in addition tophotoacid generators.

Other minor components that may be present in the overlying layerinclude bases, surfactants, dissolution inhibitors, sensitizers, coatingenhancers and other compounds known to those skilled in the art.

Suitable acid generators that may be present in the overlying layerinclude triflates (e.g., triphenylsulfonium triflate orbis-(t-butylphenyl) iodonium triflate), pyrogallol (e.g., trimesylate orpyrogallol), onium salts such as a triarylsulfonium and diaryl iodoniumhexafluoroantimates, hexafluoroarsenates, trifluoromethane sulfonatesand others; iodonium sulfonates and trifluoromethanesulfonate esters ofhydroxyamines, alpha′-bis-sulfonyl diazomethanes, sulfonate esters ofnitro-substituted benzyl alcohols and napthoquinone-4-diazides and alkyldisulfonates. Other suitable acid generators for use in the overlyinglayer are disclosed, for example, in U.S. Pat. Nos. 5,045,431 and5,071,730 both to Allen, et al. and Reichmanis, et al. review article(Chemistry of Materials, Vol. 3, page 395 (1991), the disclosures ofwhich are incorporated herein by reference.

The overlying photoresist composition employed in the present inventionmay also include any suitable crosslinking agent known in the negativephotoresist art which is otherwise compatible with the other selectedcomponents of the photoresist composition. The crosslinking agentspreferably act to crosslink the polymer component in the presence of agenerated acid. Preferred crosslinking agents are glycoluril compoundssuch as tetramethoxymethyl glycoluril, methylpropyltetramethoxymethylglycoluril, and methylphenyltetramethoxymethylglycoluril, availableunder the POWDERLINK trademark from American Cyanamid Company. Otherpossible crosslinking agents include: 2,6-bis(hydroxymethyl)-p-cresol,compounds having the following structures:

wherein R₁₃ is CH₃ or CH₂CH₃; and R₁₄ and R₁₅ are each independently aC₁-C₈ alkyl or aryl hydrocarbon;

including their analogs and derivatives, such as those found in JapaneseLaid-Open Patent Application (Kokai) No. 1-29339, as well as etherifiedamino resins, for example methylated or buylated melamine resins(N-methoxymethyl-or N-butoxymethyl-melamine respectively) ormethylated/butylated glycolurils, for example as can be found inCanadian Patent No. 1 204 547. Combinations of crosslinking agents mayalso be used.

In addition to the above components, the overlying photoresistcompositions of the present invention generally include a castingsolvent to dissolve the other components so that the overall compositionmay be applied evenly onto the surface of the underlayer to provide adefect-free coating. The solvent used in the overlying photoresist layerpreferably does not appreciably dissolve the materials present in theunderlayer, since otherwise unwanted intermixing may occur. Examples ofsuitable casting solvents include: ethoxyethylpropionate (“EEP”), acombination of EEP and γ-butyrolactone (“GBL”),propylene-glycolmonoethylether acetate (PGMEA), and ethyl lactate. Thepresent invention is not limited to selection of any particular solvent.

Examples of bases include: dimethylamino pyridine,7-diethylamino-4-methyl coumarin (“Coumarin 1”), tertiary amines, protonsponge, berberine, and the polymeric amines as in the PLURONIC orTETRONIC series from BASF. Tetra alkyl ammonium hydroxides orcetyltrimethyl ammonium hydroxide may be used as a base additive, aswell.

Examples of possible surfactants include fluorine-containing surfactantssuch as FLUORAD FC-430 available from 3M Company in St. Paul, Minn., andsiloxane-containing surfactants such as the SIL WET series availablefrom Union Carbide Corporation in Danbury, Conn.

Examples of sensitizers include: chrysenes, pyrenes, fluoranthenes,anthrones, benzophenones, thioxanthones, and anthracenes, such as9-anthracene methanol (9-AM). Additional anthracene derivativesensitizers are disclosed in U.S. Pat. No. 4,371,605. The sensitizer mayinclude oxygen or sulfur. The preferred sensitizers will be nitrogenfree, because the presence of nitrogen (e.g., an amine or phenothiazinegroup) tends to sequester the free acid generated during the exposureprocess resulting in loss of photosensitivity.

The overlying photoresist compositions of the present invention are notlimited to any specific proportions of the various components. Where theoverlying photoresist compositions of the present invention contain asolvent, the compositions preferably contain about 5 to 50 wt. % solids.The amount of acid generator present in the overlying layer ispreferably about 1 to 20 wt. % based on the weight of the polymercomponent. The amount of crosslinking agent present in the overlyinglayer is preferably about 1 to 30 wt. % based on the weight of thepolymer component, more preferably about 5 to 25 wt. %.

The above description describes the various components of the underlayerand overlying photoresist layer of the bilayer film of the presentinvention. The following description, with reference to FIGS. 1A-1D,2A-2E, and 3A-3D, describes various methods of the present invention. Inthe drawings, identical reference numerals are used to describe likematerials.

FIGS. 1A-1D illustrate one embodiment of the present invention in whichthe overlying photoresist layer is applied to the underlayer prior toimagewise exposure to radiation. Also, in the illustrated example, thetop overcoated photoresist layer need not contain a PAG. The only sourceof acid illustrated in this example may be in the underlayer.

Specifically, FIG. 1A shows a structure that is formed after applyingunderlayer 12 to a surface of substrate 10 and after applying overlyinglayer 14 to a surface of underlayer 12. The compounds of the underlayerare typically admixed prior to the application thereof to substrate 10.The substrate may be any semiconductor substrate, any conductivematerial, any insulating material or combinations thereof, includingmultilayers.

Examples of semiconductor materials include, but are not limited to: Si,SiGe, SiC, SiGeC, GaAs, InAs, InP and other III/V compoundsemiconductors. The term “semiconducting” also includessilicon-on-insulators. Examples of conductive materials include, but arenot limited to: polysilicon, metals, metal alloys, and metal silicides.Illustrative examples of insulating materials include, but are notlimited to: oxides, nitrides and oxynitrides.

The substrate may be cleaned by standard processes well known to thoseskilled in the art prior to applying the underlayer 12 to the surface ofsubstrate 10. The underlayer may be coated onto the substrate usingart-known techniques such as spin-on coating, spray coating, brushing,dip coating or by a doctor blade. After application of the underlayer,the underlayer is typically heated to an elevated temperature of about100° to about 250° C. for a short period of time of from about 1 toabout 30 minutes to drive off solvent and optionally induce thermalcrosslinking of the underlayer. The dried underlayer generally has athickness of from about 0.01 to about 1 micron, with a thickness of fromabout 0.03 to 1 micron being more highly preferred.

The overlying layer is then applied to the underlayer using one of theabove mentioned coating processes. A heating step may also follow theapplication of the overlying layer. When a heating step is employed atthis point, the heating is performed at an elevated temperature of about100° to about 150° C. for a short period of time of from about 1 toabout 30 minutes to drive off solvent present in the overlying layer.The final overlying layer after coating and heating has a thickness offrom about 0.1 to about 10 microns, with a thickness of from about 0.1to about 1 microns being more highly preferred.

Next, the film shown in FIG. 1A is imagewise exposed to radiation,suitably electromagnetic radiation or electron beam radiation,preferably ultraviolet radiation suitably at a wavelength of about150-365 nm, preferably 157 nm, 193 or 248 nm. In some embodiments, EUVradiation (13 nm) may be employed. Suitable radiation sources includemercury, mercury/xenon, xenon lamps, excimer lasers and soft x-raysources. The preferred radiation source is an ArF excimer laser, a KrFexcimer laser or a F₂ laser.

FIG. 1B illustrates the structure during the imagewise exposure step. Asshown, the arrows designated by reference numeral 16 represent theapplied radiation, reference numeral 18 denotes a photomask that is usedto provide a desired pattern in the bilayer film of the presentinvention, and reference numeral 20 denotes the latent photoacid imageformed in underlayer 12 during the exposure step. That is, region 20denotes the area in which the acid is generated in the underlayer.

After the bilayer film has been exposed to radiation, the film is heatedto an elevated temperature of from about 90° to about 160° C. for ashort period of about 1 minute or less. This heating step of the presentinvention causes a chemical transformation in the overlying layer, e.g.,deprotection, and diffusion of photoacid from the underlying layer intothe overlying layer. The resultant structure that is formed after theheating step is illustrated in FIG 1C. In this figure, reference numeral22 denotes the area of vertical up-diffusion of PAG that is generated inthe bilayer film of the present invention. As shown, the photoacid ispresent in the imagewise exposed portions essentially continuously fromthe top surface of the overlying layer down to the interface that isformed between the underlayer and the overlying layer. As is alsoillustrated in FIG. 1C, the vertical up-diffusion of photoacid is thesole mechanism for image formation within the overlying layer 14.

FIG. 1D shows the step of developing the image into the overlying layerby utilizing a conventional resist developer. Reference numeral 24denotes the patterned image formed into the overlying layer. Suitableresist developers for developing a high contrast positive image includean aqueous base, preferably an aqueous base without metal ions such astetramethylammonium hydroxide or choline. As shown in this example, thedevelopment results in the removal of the exposed areas of the overlyingfilm.

In other embodiments (not shown), the unexposed portions of theoverlying layer is removed utilizing a developer solution that iscapable of removing the unexposed regions from the overlying layer.

After providing the structure shown in FIG. 1D, the developed image istransferred through the underlayer into the substrate by knowntechniques. Preferably, the image is transferred by etching withreactive ions such as plasma etching and reactive ion etching. Suitableplasma tools include electron cyclotron resonance (ECR), helicon,inductively coupled plasma (ICP) and transmission coupled-plasma (TCP)systems. Suitably, oxygen reactive ion etching (magnetically induced) isutilized to transfer the image through the underlying layer. Etchingtechniques and equipment are well known in the art. The developed filmhas high aspect ratio, enhanced resolution, and substantially verticalwall profiles.

The bilayer film of the present invention may be used to make anintegrated chip assembly such as an integrated circuit chip, multichipmodule, circuit board, or thin film magnetic heads.

FIGS. 2A-2E illustrates another embodiment of the present invention. Inthis embodiment, the underlayer is imagewise exposed prior toapplication of the overlying photoresist layer. Specifically, FIG. 2Aillustrates a structure which includes underlayer 12 applied to asurface of substrate 10. Next, and as shown in FIG. 2B, the structureshown in FIG. 2A is imagewise exposed to a pattern of radiation. Asshown, the arrows designated by reference numeral 16 represent theapplied radiation, reference numeral 18 denotes a photomask that is usedto provide a desired pattern in the structure, and reference numeral 20denotes the latent photoacid image formed in underlayer 12 during theexposure step. Note that acid is generated in the underlayer during thisstep of the present invention.

After exposing the structure to radiation, overlying layer 14 is appliedto the underlayer containing latent photacid image 20 (see FIG. 2C), andthen the structure is heated as described above with respect to thefirst embodiment to cause acid up-diffusion and deprotection of thepolymer resin in the overlying photoresist composition (see FIG. 2D). InFIG. 2D, reference numeral 22 denotes the area of vertical up-diffusionof photoacid that is generated in the bilayer film. As shown, thegenerated acid is present essentially continuously from the top surfaceof the overlying layer down to the interface between the underlayer andthe overlying layer.

The imagewise pattern may then be transferred through the underlayerinto the substrate using the techniques described above.

FIGS. 3A-3D shows a further embodiment of the present invention. Thisembodiment is similar to the embodiment shown in FIGS. 1A-1D except thatthe overlying layer includes a PAG material itself. In this embodiment,the PAG material present in the overlying layer is different from thePAG present in the underlayer. In particular, the PAG present in theunderlayer generates an acid that has a higher diffusivity than the acidgenerated by the PAG in the overlying layer. Moreover, the acidgenerated in the underlayer should generally have an equal or lessacidity than that generated in the overlying layer.

FIG. 3A illustrates the structure that is formed after the inventivebilayer is applied to a surface of substrate 10. The bilayer includesunderlayer 12 and overlying photoresist layer 14 which includes aphotoacid generator.

FIG. 3B shows the structure during imagewise exposure. As shown, thearrows designated by reference numeral 16 represent the appliedradiation, reference numeral 18 denotes a photomask that is used toprovide a desired pattern in the bilayer film of the present invention,and reference numerals 20 and 21 denote the latent photoacid imageformed in underlayer 12 and overlying layer 14, respectively, during theexposure step. Note that acid is generated in both layers of the bilayerfilm during this step.

Next, the structure is heated as described above in the first embodimentto cause acid up-diffusion and deprotection of the polymer resin in theoverlying photoresist composition (see FIG. 3C). In FIG. 3C, referencenumeral 22 denotes the area of vertical up-diffusion of photoacid thatis generated in the bilayer film of the present invention. As shown, thegenerated acid is present essentially continuously from the top surfaceof the overlying layer down to the interface between the underlayer andthe overlying layer. FIG. 3D shows the resultant structure afterdeveloping the pattern into the overlying photoresist layer.

The imagewise pattern may then be transferred through the underlayerinto the substrate using the techniques described above.

In each of the above described embodiments, thermally driven verticalacid transportation is occurring. Previous studies on top surface imagedresist systems have shown that the extent of vertical photoaciddiffusion varies over a wide range and is a strong function of thespecific polymer:PAG combinations (see G. Wallraff, et al., Proc. SPIE1999, 3678, 138). The thickness and transparency of the film to bepatterned will dictate the properties of the PAG employed in theunderlayer of the present invention. Resolution can be controlled in thepresent invention to some extent by controlling the thickness of theoverlying layer and/or through the incorporation of bases or otheradditives.

In the second embodiment of the present invention mentioned above, theabsorbance of the overlying photoresist layer is not an issue sinceimaging occurs prior to coating of the overcoat layer. Thus, an opaquepolymer resin may be employed. The absence of a PAG in the polymer resinof the overcoat layer in the first embodiment described above alsocontributes to transparency. In the case of a highly absorptive overcoatphotoresist such as the case in the third embodiment described above,the presence of a mobile photoacid generated in the underlayer diffusingupward will minimize the impact of low light levels at the bottom of theoverlying layer. In addition, there are other potential methods forcontrolling lateral acid diffusion including, but not limited to: theuse of a basic or other additives in both the underlayer and theoverlying layer, as well as the use of photodecomposable bases in theoverlying layer, optimization of the bake temperatue, time, ramptemperature rate, etc.

The present invention thus provides a new imaging technology that isbased on vertical acid transport. The surprising level of image fidelity(higher resolution imaging) observed when employing the methods of thepresent invention suggest that the present invention may be useable as areplacement for conventional lithographic imaging in some applications.

The following examples are provided to illustrate the method of thepresent invention and to illustrate some advantages that can be obtainedusing the same.

EXAMPLE 1

An underlayer composition of the present invention was prepared bymixing 72.8 mg of bis-t-butylphenyl iodonium ditrifluoromethanesulfonylimide with 10 gm of AR 19 antireflection coating (Shipley Co.). Thiscomposition was spin coated onto a silicon substrate 200 mm in diameterand baked on a hot plate at 180° C. for 90 seconds. The resulting filmthickness was 80 nm. On top of this composition was coated a prototype157 nm photoresist based on an aromatic fluoroalcohol as described inWallraff, et al. in Proc. SPIE 1999, 3678, 138 (the contents of whichare incorporated herein by reference) with an absorbance of 3.6microns⁻¹ at 157 nm. This resist was coated at a thickness of 135 nm andbaked on a hot plate at 130° C. for 60 seconds.

The film was exposed to F₂ laser radiation (157 nm) with an EXITECHstepper through a binary mask patterned with a 150 nm line/space arrayat doses ranging from 5-30 mJ/cm² and baked on a hot plate at 130° C.for 30 seconds and developed in LDD-26 for 60 seconds. Clean developmentwas observed at a dose of 21 mJ/cm² for a 150 nm 1/s array (see FIG.4A).

COMPARATIVE EXAMPLE 1

An underlayer comprising AR 19 antireflection coating (Shipley Co.)without any photoacid generator was spin coated into a silicon substratehaving a 200 mm diameter and baked in a hot plate at 180° C. for 3minutes. The resulting film thickness was 80 nm. Over this compositionwas coated a prototype 157 nm photoresist based on an aromaticfluoroalcohol as described in Wallraff, et al. in Proc. SPIE 1999, 3678,138 (the contents of which are incorporated herein by reference) with anabsorbance of 3.6 micron⁻¹ at 157 nm. This resist was coated at athickness of 135 nm and baked on a hot plate at 130° C. for 60 seconds.

The film was exposed to F₂ laser radiation (157 nm) with an EXITECHstepper through a binary mask patterned with a 150 nm line/space arrayat doses ranging from 5-30 mJ/cm² and baked on a hot plate at 130° C.for 30 seconds and developed in CD-26 for 60 seconds. The resist did notclear under any exposure conditions and approximately ⅓ of the resistfilm remained at the dose to size for 150 nm line/space arrays (see FIG.4B).

EXAMPLE 2

Another underlayer composition of the present invention was prepared bymixing 72.8 mg of iso-t-butylphenyl iodonium ditrifluoromethanesulfonylimide with 10 gm of AR 19 antireflection coating (Shipley Co.). Thiscomposition was spin coated onto a silicon substrate having a diameterof 125 nm and baked on a hot plate at 180° C. for 3 minutes. Theresulting film thickness was 80 nm. Over this composition was coated aprototype 157 nm polymer (lacking a photoacid generator) based on anaromatic fluoroalcohol as described in Wallraff, et al. in Proc. SPIE1999, 3678, 138 (the contents of which are incorporated herein byreference) with an absorbance of 0.3 microns⁻¹ at 248 nm.

This polymer resist was coated at a thickness of 135 nm baked on a hotplate at 130° C. for 60 seconds. The film was exposed to KrF laserradiation (248 nm) with an Nikon stepper through a binary mask patternedwith a 250 nm line/space array at doses ranging from 5-20 mJ/cm² andbaked on a hot plate at 130° C. for 30 seconds and developed in CD-26for 60 seconds. The smallest features resolved were 250 nm. Finalthickness of the patterned resist film, wherein the only source ofphotoacid generator was from the PAG in the underlayer, wasapproximately 100 nm.

COMPARATIVE EXAMPLE 2

An underlayer comprising AR 19 antireflection coating (Shipley Co.)without any photoacid generator was spin coated onto a silicon substratehaving a diameter of 125 nm and baked on a hot plate at 180° C. for 3minutes. The resulting film thickness was 80 nm. Over this compositionwas coated a prototype 157 nm resist (containing a photoacid generator)based on an aromatic fluoroalcohol as described in Wallraff, et al. inProc. SPIE 1999, 3678, 138 (the contents of which are incorporatedherein by reference) with an absorbance of 0.3 micron⁻¹ at 248 nm.

This polymer resist was coated at a thickness of 135 nm baked on a hotplate at 130° C. for 60 seconds. The film was exposed to KrF laserradiation (248 nm) with a Nikon stepper through a binary mask patternedwith a 250 nm line/space array at doses ranging from 2.5-30 mJ/cm² andbaked on a hot plate at 130° C. for 30 seconds and developed in CD-26for 60 seconds. The smallest features resolved were 250 nm. Finalthickness of the patterned resist film, wherein the only source ofphotoacid generator was from the PAG in the underlayer, wasapproximately 125 nm.

EXAMPLE 3

A preferred underlayer composition of the invention was prepared bymixing 123.2 mg of triphenyl sulfonium ditrifluoromethanesulfonyl imidewith 10 grams of DUV30 antireflection coating (Brewer Science). Thiscomposition was spin coated onto a silicon substrate (200 mm indiameter) and baked on a hot plate at 180° C. for 90 sec. The resultingfilm thickness was 80 nm. On top of this composition was coated aprototype 157 nm photoresist (containing a photoacid generator) based onan aromatic fluoroalcohol as described in Wallraff, et al. in Proc. SPIE1999, 3678, 138, with an absorbance of 3.6/micron at 157 nm. This resistwas coated at a thickness of 135 nm and baked on a hot plate at 130° C.for 60 sec. The film stack was exposed to F₂ laser radiation (157 nm)with a high NA EXITECH stepper through a binary mask patterned with a 90nm line/space array at doses ranging form 5-30 mJ/cm² and baked on a hotplate at 130° C. for 30 sec. and developed in LDD-26 for 60 sec. Cleandevelopment was observed at a dose of 8.7 mJ/cm² for a 90 nm 1/s array(see FIG. 5).

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in forms and details maybe made herein without departing from the spirit and scope of theinvention. It is therefore intended that the present invention is notlimited to the exact forms and details described and illustrated, butfall within the scope of the appended claims.

1. A bilayer film comprising: (A) an underlayer located upon asubstrate, the underlayer comprising (i) a bis-t-butylphenyl iodoniumditrifluoromethanesulfonyl amide photoacid generator and (ii) apolymeric material that includes at least one of an organic polymer andan inorganic matrix material, wherein said photoacid generator isselected for solely vertical transport of generated acid into anoverlying layer; and (B) the overlying layer located upon saidunderlayer and further spaced from the substrate, said overlying layercomprising an organic polymer containing acid reactive groups suitablefor use in chemically amplified photoresists, wherein said overlyinglayer is substantially free of a photoacid generator.
 2. The bilayerfilm of claim 1 wherein: the photoacid generator is present in an amountof from about 0.5 to about 20 weight percent, based on the total weightof component A.
 3. The bilayer film of claim 1 wherein the organicpolymer of said underlayer is selected from hard bakeddiazonapthoquinone novalac, polyimides, polyethers, polyacrylates, andantireflective coating formulations.
 4. The bilayer film of claim 1wherein the organic polymer of said underlayer is a crosslinking acrylicpolymer.
 5. The bilayer film of claim 1 wherein the inorganic matrixmaterial is selected from a silsesquioxane, hydridosilsesquioxane,methylsilsesquioxane and other Si-containing polymers.
 6. The bilayerfilm of claim 1 wherein component A further comprises a solvent.
 7. Thebilayer film of claim 1 wherein the organic polymer of said overlyinglayer includes a monomer selected from a phenolic-containing resin, apolymer having acid or an anhydride group, an acrylamide, an imide and ahydroxyimide.
 8. The bilayer film of claim 1 wherein the organic polymerof said overlying layer comprising two or monomer units is selected fromhydroxystyrenes, styrenes, acrylates, acrylic acid, methacrylic acid,vinylcyclohexanol, phenol formaldehydes, methacrylates, acrylamides,maleic anhydride and maleimides.
 9. The bilayer film of claim 1 whereinthe acid reactive groups are selected from the group consisting ofesters, carbonates, ketals, silyl ethers and mixtures thereof.
 10. Thebilayer film of claim 1 wherein said acid reactive groups are reactivemoieties that undergo a crosslinking reaction.
 11. The bilayer film ofclaim 1 wherein the overlying layer further comprises a crosslinkingagent.
 12. The bilayer film of claim 1 wherein the overlying layerincludes a dissolution inhibitor.
 13. A bilayer film comprising: (A) anunderlayer located upon a substrate, the underlayer comprising (i) aphotoacid generator and (ii) a polymeric material that includes at leastone of an organic polymer and an inorganic matrix material, wherein saidphotoacid generator is selected for solely vertical transport ofgenerated acid into an overlying layer; and (B) the overlying layerlocated upon said underlayer and further spaced from the substrate, saidoverlying layer comprising a positive-tone photoresist organic polymercontaining acid reactive groups suitable for use in chemically amplifiedphotoresists, wherein said overlying layer is substantially free of aphotoacid generator.
 14. The bilayer film of claim 1 wherein theoverlying layer is a negative-tone photoresist.
 15. An imagewisedexposed product including at least the bilayer film of claim
 1. 16. Theimagewised exposed product of claim 15 wherein said vertical transportof said generated acid provides a substantially continuous latent imageof acid in said overlying layer.
 17. An imagewised exposed productincluding at least the bilayer film of claim
 13. 18. A bilayer filmcomprising: (A) an underlayer located upon a substrate, the underlayercomprising (i) a photoacid generator and (ii) a polymeric material thatincludes at least one of an organic polymer and an inorganic matrixmaterial, wherein said photoacid generator is selected for solelyvertical transport of generated acid into an overlying positive-tonephotoresist layer; and (B) the overlying positive-tone photoresist layerlocated upon said underlayer and further spaced from the substrate, saidoverlying positive-tone photoresist layer comprising an organic polymercontaining acid reactive groups suitable for use in chemically amplifiedphotoresists, wherein said overlying layer is substantially free of aphotoacid generator.
 19. An imagewised exposed product including atleast the bilayer film of claim 18.